Military Standards set forth Test Methods and Procedures for Microelectronics for Hermetically Seal of Microelectronic Devices. The purpose of the test procedure is to determine the effectiveness, or the hermeticity of the seal, of microelectronic devices with designed internal cavities. Apparatus required for testing the seal of the package shall consist of suitable pressure and vacuum chambers and a mass spectrometer type preset and properly calibrated for a helium leak rate sensitivity sufficient to read measured helium leak rate of 10.sup.-9 atm cc/sec and greater. The leak detector indicator shall be calibrated using a diffusion type certified standard leak, at least one during every working shift. Test procedure requires the package shall be placed in a sealed chamber, which is then pressurized with a tracer gas of 100 percent helium for the required time and pressure. The bomb pressure shall be 75 psig minimum, exposure time shall be one hour minimum and the device shall be measured within 30 minutes after it has been removed from the pressure vessel. Devices with an internal cavity volume of 0.1 cc or less shall be rejected if the measured tracer gas leak rate exceeds 5.times.10.sup.-8 atm cc/sec. Devices with an internal cavity volume greater than 0.1 cc shall be rejected, if the measured tracer gas leak rate exceeds 5.times.10.sup.-7 atm cc/sec.
In the present invention the bases of the microcircuit and lids are placed in a vacuum bake oven (125C) for 24 hours to remove the moisture from the microcircuit. The microcircuits are moved into a controlled environment of tracer gas comprised of 5 percent helium and 95 percent nitrogen. Package is then placed in the welding machine (while in the helium-nitrogen environment) where the lid is fusion welded to the base of the package to retain the helium-nitrogen mixture therein. The package is placed in a Pneumatic Gross Leak Tester. Packages that pass the Pneumatic Gross Leak Test are moved into the fine leak test environment of 100 percent nitrogen.